In European countries, thermostats generally use a bimetallic strip to sense temperature and respond to temperature changes in the room. The movement of the bimetallic strip is used to directly open and close an electrical circuit. Power is delivered to an electromechanical actuator, usually relay or contactor in the boiler equipment whenever the contact was closed to provide heating and/or cooling to the controlled space. Since these thermostats do not require electrical power to operate, the wiring connections were very simple. A two-wire connection typically runs between the thermostat and the boiler system.